1. Field of the Invention
The present invention relates to a field emission display (FED) device, and more particularly to an FED device using nano-sized electron emitters having low power consumption.
2. Description of Prior Art
In recent years, flat panel display devices have been developed and widely used in electronic applications such as personal computers. One popular kind of flat panel display device is an active matrix liquid crystal display (LCD) that provides high resolution. However, the LCD has many inherent limitations that render it unsuitable for a number of applications. For instance, LCDs have numerous manufacturing shortcomings. These include a slow deposition process inherent in coating a glass panel with amorphous silicon, high manufacturing complexity, and low yield of units having satisfactory quality. In addition, LCDs require a fluorescent backlight. The backlight draws high power, yet most of the light generated is not viewed and is simply wasted. Furthermore, an LCD image is difficult to see under bright light conditions and at wide viewing angles. Moreover, since the response time of an LCD is dependent upon the response time of a liquid crystal to an applied electrical field, the response time of the LCD is correspondingly slow. A typical response time of an LCD is in the range from 25 ms to 75 ms. Such difficulties limit the use of LCDs in many applications such as High-Definition TV (HDTV) and large displays. Plasma display panel (PDP) technology is more suitable for HDTV and large displays. However, a PDP consumes a lot of electrical power. Further, the PDP device itself generates too much heat.
Other flat panel display devices have been developed in recent years to improve upon LCDs and PDPs. One such flat panel display device, a field emission display (FED) device, overcomes some of the limitations of and provides significant advantages over conventional LCDs and PDPs. For example, FED devices have higher contrast ratios, wider viewing angles, higher maximum brightness, lower power consumption, shorter response times and broader operating temperature ranges when compared to conventional thin film transistor liquid crystal displays (TFT-LCDs) and PDPs.
One of the most important differences between an FED and an LCD is that, unlike the LCD, the FED produces its own light source utilizing colored phosphors. The FED does not require complicated, power-consuming backlights and filters. Almost all light generated by an FED is viewed by a user. Furthermore, the FED does not require large arrays of thin film transistors. Thus, the costly light source and low yield problems of active matrix LCDs are eliminated.
In an FED device, electrons are extracted from tips of a cathode by applying a voltage to the tips. The electrons impinge on phosphors on the back of a transparent cover plate and thereby produce an image. The emission current, and thus the display brightness, is highly dependent on the work function of an emitting material at the field emission source of the cathode. Conventional FED devices employ metal microtips as the emitting material. However, it is difficult to precisely fabricate extremely small metal microtips for the field emission source. In addition, it is necessary to maintain the inside of the electron tube at a very high vacuum of about 10xe2x88x927 Torr, in order to ensure continued accurate operation of the microtips. The very high vacuum required greatly increases manufacturing costs. Furthermore, a typical FED device needs a high voltage applied between the cathode and the anode, commonly in excess of 1000 volts.
Recently, carbon nano-tubes have been increasingly suggested as having the most potential to overcome the aforementioned disadvantages of conventional field emission sources. Carbon nano-tubes can accurately concentrate electrons emanating from a field emission source, and are chemically stable and mechanically sturdy. U.S. Pat. No. 6,339,281 discloses an FED device employing carbon nano-tubes as emitters. As shown in FIG. 5, the FED device comprises a glass substrate 91, a cathode electrode 92 formed on the glass substrate 91, a base layer 93 deposited on the cathode electrode 92, and carbon nano-tubes 95 formed on a catalyst layer 94 formed on the base layer 93. A material of the base layer 93 has good conductivity, for providing effective electrical contact between the cathode electrode 92 and the carbon nano-tubes 95. However, when emission voltage is applied to the nano-tubes, electrons are emitted not only from the nano-tubes but also from the base layer. It is difficult to control the emitted electrons, which adversely affects the quality of the display produced.
In view of the above-described drawbacks, an object of the present invention is to provide a field emission display (FED) device which has low power consumption.
Another object of the present invention is to provide an FED device which has accurate and reliable electron emission.
In order to achieve the objects set out above, an FED device in accordance with a preferred embodiment of the present invention comprises a cathode plate, an electrically resistive buffer made from carbon formed on the cathode plate, a plurality of electron emitters made from carbon formed on the buffer, and an anode plate spaced from the electron emitters thereby defining an interspace region therebetween. Each electron emitter comprises a nano-rod. The combined buffer and electron emitters has a gradient distribution of electrical resistivity such that highest electrical resistivity is nearest the cathode plate and lowest electrical resistivity is nearest the anode plate. When emitting voltage is applied between the cathode and anode plates, electrons emitted from the electron emitters traverse the interspace region and are received by the anode plate. Because of the gradient distribution of electrical resistivity, only a very low emitting voltage needs to be applied.
In alternative embodiments, each electron emitter comprises a carbon nanotube that has uniform electrical resistivity. Only the buffer has a gradient distribution of electrical resistivity. The nanotube may be a single walled nanotube or a multi-walled nanotube.
In still further alternative embodiments, the buffer and/or the electron emitters can incorporate more than one gradient distribution of electrical resistivity.
Other objects, advantages and novel features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: